1. Field of the Invention
This invention relates to vehicle navigation systems especially those for low-flying aircraft.
2. Description of the Prior Art
At present, self contained systems for finding the position of an aircraft fall into two main types: inertial navigation systems and radar systems.
Inertial navigation systems operate by using accelerometers arranged to sense the aircraft's acceleration along three orthogonal axes. These accelerations are then integrated to provide a measure of the aircraft's velocity and displacement from its starting position.
Radar systems operate by transmitting radar signals to the terrain around the vehicle and then using the reflected signals to produce a map of this terrain. This map is then compared with a pre-recorded map of the area and the aircraft position is taken to be the one at which the two maps correspond most closely.
Radar systems have the disadvantage that they require the aircraft to transmit radar signals, which can of course be picked up by anyone with a suitable receiver: in military aircraft this is of course highly undesirable.
Both systems have the problem that they are heavy and expensive. In aircraft generally and especially in remotely piloted aircraft weight is very important because the aircraft payload is limited.